In a D2D (Device-to-Device) communication environment, each node such as a mobile phone searches for another node physically adjacent to the node by itself, configures a communication session, and then directly transmits traffic to the counterpart node. Accordingly, the D2D communication distributes traffic concentrated on an evolved NodeB (eNB), and thus is spotlighted as an element technology of a next generation mobile communication technology, which can solve a traffic overload problem. Accordingly, a standardization organization such as 3GPP (3rd Generation Partnership Project) or IEEE (Institute of Electrical and Electronic Engineers) proceeds with a D2D communication standard based on LTE-A (Long Term Evolution-Advanced) or Wi-Fi (Wireless Fidelity).
In order to perform the D2D communication, a frame structure, a signal procedure, a scheduling procedure, and the like for direct communication between terminals should be defined in detail. Particularly, it is important to exclude interference to a cellular system or interference to D2D communication by other terminals. Accordingly, a technology, which has been known as the D2D communication, includes “FlashLinQ” of Qualcomm. The FlashLinQ defines a physical layer channel structure, a scheduling procedure, and the like for the D2D communication. Further, the FlashLinQ measures channel quality between terminals to perform the D2D communication for the scheduling procedure, and defines a reference for determining whether to perform communication based on the channel quality. More specifically, in the FlashLinQ, a transmission terminal transmits a DPS (Direct Power Signal) through an inherent single tone allocated to the transmission terminal and estimates received power and a SIR (Signal to Interference Ratio) through the DSP. Further, whether to perform the communication is determined based on the received power and the SIR.
As described above, whether to perform the communication is determined based on the signal transmitted through the single tone. Thereafter, the D2D communication is performed using a whole band for the D2D communication. That is, data communication through the whole band is performed based on channel quality estimated through the signal of the single tone. However, the channel quality estimated through the signal of the single tone provides inaccurate channel quality information on the whole band depending on a channel environment. For example, in a multi-path channel environment, there may be a large difference between reception channel power of the single tone and reception channel power of the whole band due to an influence of frequency selective fading. For example, the inaccurate measurement of the reception channel power is illustrated in FIG. 1. FIG. 1 illustrates an example of a result of channel measurement using a single tone power signal. Referring to FIG. 1, a terminal A 111 receives a DPS transmitted from each of a terminal B 112, a terminal C 113, and a terminal D 114 and estimates reception channel power. At this time, the terminal B 112, the terminal C 113, and the terminal D 114 transmit the DPSs through the single tone. Accordingly, depending on a frequency of the single tone, a measurement result different from average channel power may be made. Referring to FIG. 1, in a case of the terminal B 112, channel power lower than the average channel power may be measured using a frequency having channel power lower than the average channel power. However, in a case of the terminal C 113, channel power higher than the average channel power may be measured using a frequency having channel power higher than the average channel power.
As described above, by estimating the channel quality through the single tone power signal, a result different from the channel quality of the whole band may be created. In this case, when an SIR for an actual whole band is considered by inaccurate channel quality information, communication may be abandoned due to a measurement error even though the communication is possible. Alternatively, even though it is difficult to perform the communication, a scheduling process error, which attempts the communication due to a measurement error, may be generated. When the scheduling error is generated, a problem in terms of fairness may occur and also a transmission rate loss for entire cells may be caused.